1. Field of the Invention
This invention relates generally to nonvolatile random access magnetic memory devices. More particularly, the present invention relates to an improved Hall effect ferromagnetic random access memory cell and its method of fabrication.
2. State of the Art
The Hall effect is an electromagnetic phenomenon whereby a conductor carrying an electric current perpendicular to an applied magnetic field develops a voltage gradient which is transverse to both the current and the magnetic field. This principle has been applied in many electromagnetic devices, including those constructed with semiconducting materials to produce field effect transistors (FETs).
FETs are well known and have been used to create digital memory devices. For example, U.S. Pat. No. 5,295,097 to Lienau teaches a Hall effect memory device comprising a domain made of ferromagnetic material, substantially surrounded by a conducting coil. When the coil is supplied with an electric current, a residual magnetic field is created in the domain, the polarity of this magnetic field depending on the direction of the current of the coil. This is how digital information is written to the domain. A FET is disposed so as to be perpendicularly penetrated by this field, the differential voltage across the drains of the FET indicating the polarity of the magnetic field. This is how digital information is read from the domain.
While these devices are known in the art, they are somewhat difficult and costly to construct. Additionally, fabrication constraints affect the density of placement of the devices on a computer chip, and thus affect the overall size of digital computer components. It would be desirable to have a hall effect ferromagnetic random access memory device that is less expensive and less difficult to fabricate, and which is also smaller and may be disposed on a microchip in greater density.
It is therefore an object of the present invention to provide a Hall effect ferromagnetic random access memory cell that is easier and less expensive to mass produce than other such devices.
It is another object of the invention to provide a Hall effect ferromagnetic random access memory cell that provides better signal sensing capabilities than other such devices.
It is another object of the invention to provide a method of mass producing such cells that is easier and less expensive to mass produce than prior devices.
It is yet another object of the invention to provide a random access memory circuit that is comprised of a matrix of Hall effect ferromagnetic random access memory cells constructed according to this invention.
It is another object of the invention to provide Hall effect ferromagnetic random access memory cells that are reproducible in their behavior and give a high yield.
The above and other objects are realized in a method of manufacturing a Hall effect ferromagnetic non-volatile random access memory cell comprising the steps of providing a piece of substrate material; depositing upon the surface of the substrate a Hall sensor material; depositing upon the surface of the substrate interconnect lines for electrically connecting the Hall sensor material to its source and drains; depositing upon the Hall sensor material and the interconnect lines a first layer of insulating material; depositing upon the first layer of insulating material a thin layer of ferromagnetic material; depositing an additional desired thickness of ferromagnetic material upon the thin layer of ferromagnetic material; forming the ferromagnetic material into a magnetically polarizable domain having a long axis substantially perpendicular or normal to the plane of the substrate; depositing upon the ferromagnetic material a second layer of insulating material; depositing upon the second layer of insulating material a thin layer of electrically conductive material by means of electron beam deposition, sputtering, or other thin film deposition technique; depositing on the thin layer of electrically conductive material an additional desired thickness of electrically conductive material by the process of electroplating; forming the electrically conductive material into a coil substantially surrounding the length of the domain and configured to produce a residual magnetic field therein when an electrical current is applied to the coil; depositing upon the surface of the electrically conductive material and the second layer of insulating material interconnect lines for uniquely electrically connecting the coil to a bit write line and a word write line; and coating the entire cell structure with a passivation layer.
These and other objects are also realized in a Hall effect ferromagnetic non-volatile random access memory apparatus comprising a substrate having a plurality of elongate, magnetically polarizable domains oriented with their long axis substantially normal to the substrate. A plurality of word write lines and bit write lines are also carried by the substrate, and a plurality of conductive coil members are connected thereto, each between one of the word write lines and one of the bit write lines and substantially surrounding and being coupled to one of the domains and having a central axis oriented substantially parallel to the long axis of the domains. A current source is connected to the word write lines and bit write lines for driving a current through a selected coil member so as to switch the residual magnetic field direction of the domain coupled thereto, and at least one magnetic field sensor is located proximate to each domain for passively sensing the direction of the residual magnetic field of that domain.
Some of the above objects are also realized in a Hall effect ferromagnetic non-volatile random access memory apparatus described above wherein the sensors comprise a field effect transistor defining a Hall effect channel connected to a pair of drains and oriented for substantially perpendicular penetration of its channel by the residual magnetic field of the adjacent domain. The memory apparatus also has a plurality of word read lines and bit read lines carried by the substrate, and each of the field effect transistors are uniquely connected with its source to one of the word read lines and each of its drains to one of the bit read lines. A current source is provided for selectively supplying a current to each of the word read lines. A comparator for comparing the voltage across each of the paired bit read lines is provided to determine the memory status of the domain.
Other objects and features of the present invention will be apparent to those skilled in the art, based on the following description, taken in combination with the accompanying drawings.